North Korean leader Kim Jong-Un, left, inspects a flight training of Korean People's Army (KPA) Air and Anti-Air Force Unit 188 on April 21 at an undisclosed place in North Korea. (AFP)

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WASHINGTON — The United States said Tuesday it was watching North Korea “very closely” following South Korean warnings that Pyongyang may be preparing a fourth nuclear test ahead of a visit to Seoul by President Barack Obama.

“North Korea has a history of taking provocative action and we are always mindful of the possibility that such an action could be taken,” White House spokesman Jay Carney told reporters aboard Air Force One as Obama departed for his week-long trip to Asia.

Carney said any action by North Korea would “most likely be in violation of numerous commitments that the DPRK (North Korea) is bound by but of course, that is something that they unfortunately have done many times.”

He declined to comment on the validity of a South Korean defense ministry briefing which cited increased activity at North Korea’s main nuclear test site.

“Our military is currently detecting a lot of activity in and around the Punggye-ri nuclear test site,” defense ministry spokesman Kim Min-Seok told reporters earlier.

“We’ll be watching it very closely,” Carney said.

Obama is due to reach Seoul on Friday during a swing through Asia which also includes stops in Japan, Malaysia and the Philippines.

North Korea slammed Obama’s Asian tour as “reactionary and dangerous” on Monday, saying it would only serve to “escalate confrontation and bring dark clouds of a nuclear arms race” over the Korean peninsula.

North Korea has carried out three nuclear tests in the past eight years — one in October 2006, another in May 2009 and a third in February 2013.